1. Field of the Invention
The present invention relates generally to a transmission for a marine vessel and, more particularly, to a marine reverse reduction gearbox which incorporates one or more variably engageable clutches, or slippable clutches, for variably transmitting torque between a prime mover and a propeller shaft of a marine vessel.
2. Description of the Prior Art
Marine reduction gearbox assemblies are used to transmit torque between a unidirectional prime mover and the propeller shaft of the marine vessel to provide bidirectional rotation capability for the propeller in association with the unidirectional prime mover. The rotational speed of the propeller shaft and the direction of the propeller shaft in a marine vessel are typically controlled by regulating the rotational speed of the prime mover in cooperation with engagement and disengagement of one or more clutches connected in torque transmitting association between the prime mover and the propeller shaft. Typically, an input shaft of a marine reduction gearbox is connectible to the prime mover and is also connected to forward and reverse transfer gears. These transfer gears continually rotate in opposite directions during operation and are driven by the prime mover. The forward and reverse transfer gears are connected, through clutches, to forward and reverse drive shafts which are, in turn, associated with individual pinion gears. The pinion gears are connected in torque transmitting association with the propeller shaft. By selectively engaging and disengaging the clutches associated with the forward and reverse transfer gears, the rotational direction of the propeller shaft can be controlled. In addition, the rotational speed of the propeller shaft can be controlled by regulating the rotational speed of the prime mover. This and many other torque transmitting techniques are known to those skilled in the art.
U.S. Pat. No. 4,451,238, which issued to Arnold on May 29, 1984, discloses a shaft brake for a marine propulsion system for a water craft. The propulsion system comprises a relatively large engine, or prime mover, and a power transmission which includes an output shaft for driving the propeller. The transmission includes forward and reverse shafts, gear trains between the forward and reverse shafts and the output shaft and clutches for the forward and reverse shafts. A shaft brake is provided to stop rotation of the output shaft for the propeller which minimizes damaging shocks to the propulsion system which sometime occur during maneuvering operations. The brake described in this patent is located concentrically with the forward shaft of the power transmission and is effective to brake the propeller shaft through interconnecting gears when both clutches are disengaged.
U.S. Pat. No. 4,458,799, which issued to Schueller on July 10, 1984, describes a marine propulsion control system that includes a maneuvering brake. The system disclosed is for air actuated ahead and astern clutches, an engine speed governor and a propeller shaft brake. The control is actuated by a throttle lever which is moved from a neutral position to select a direction of travel. The degree of movement of the throttle lever from neutral is representative of the desired speed in the selected direction. The control described in this patent engages the brake when the throttle lever is moved from an ahead to an astern direction at medium or high forward speeds. When this type of change is commanded, a pair of serially connected brake valves are piloted to connect the brake to a source of air under pressure. One of the brake valves is piloted by an accumulated speed pressure signal indicating an ahead speed greater than a predetermined minimum and the other valve is piloted by the throttle signal commanding astern direction. The brake disengages either when the accumulated pressure signal exhausts to a level below that necessary to pilot the first brake valve or when the pressure within the astern clutch rises to a preselected level.
U.S. Pat. No. 2,749,776, which issued to Fischer et al on June 12, 1956, discloses a reversing gear and a drive control that is particularly adapted for use with a marine propulsion unit. It utilizes a simplified gear arrangement in combination with clutches that control the direction in which power is transmitted. A brake is associated with the gearing in order to transmit power and to help absorb the energy of reversal upon reversal of direction of torque.
U.S. Pat. No. 4,305,710, which issued to Schneider on Dec. 15, 1981, discloses a ship propulsion transmission which has a torque converter for driving a fixed pitched propeller in the reverse direction. The transmission includes a prime mover such as a gas turbine engine or a diesel engine. It also provides a disengageable clutch between the prime mover and the propeller for the purpose of transmitting power to the propeller for driving it in a forward direction. The transmission also includes a hydraulic torque converter of the single stage, fixed housing type and which is connected between the prime mover and the propeller for driving the propeller in the reverse direction when the disengageable clutch is inoperative.
U.S. Pat. No. 4,316,722, which issued to Aschauer on Feb. 23, 1982, discloses a propulsion system for a submarine which comprises a low noise level, rapidly reversible propulsion system having a non-reversible adjustable speed prime mover, a reversible drive mechanism driven by the prime mover and a fluid-cooled torque converter and speed reduction apparatus.
U.S. Pat. No. 3,543,891, which issued to Mathers on Dec. 1, 1970, discloses a control system for engine, brake and forward-reverse clutches. It specifically describes the sequence of clutch, throttle and output shaft brake application in a propulsion system for a crash reversal condition imposed on the system. It automatically disengages the clutch assembly upon receipt of a crash reversal command signal and holds the assembly in neutral for a specific delay period before reengagement in the opposite directional mode. The control mechanism is pneumatically operated and responsive to pneumatic signals transmitted from a single lever master control.
U.S. Pat. No. 4,384,639, which issued to Collin on May 24, 1983, describes a two-way power transferring reduction gear of the epicyclic type. It includes two sun wheels, two sets of planetary gear wheels, two planetary gear wheel carriers and two external ring wheels. In addition, it also provides a means for selectively braking a first combination of one planetary gear wheel carrier and one of the external gear wheels, as well as the combination of the other external ring wheel and one of the sun wheels, respectively.
U.S. Pat. No. 3,363,732, which issued to Nakamura et al on Jan. 16, 1968, discloses a forward and reverse transmission with a brake for a prime mover. This device includes a unidirectional prime mover such as a turbine which provides a given driving force in a given direction. A transmission is connected between the prime mover and an output shaft which is connected to the load. A rearward transmission is also connected between the forward transmission and the output shaft for reversing the direction in which the latter is driven while still taking the drive in the same direction from the unidirectional prime mover.
U.S. Pat. No. 4,051,679, which issued to Collin on Oct. 4, 1977, discloses a marine propulsion plant with reversible propeller shaft connected thereto. It describes a suitable selection of the means for engaging the parts of the reversing gear in their respective working positions for both ahead and astern running, respectively. It also makes it possible to disengage the turbine part of the gear, to brake that turbine part and then to reengage the gear parts in their new relative positions.
U.S. Pat. No. 4,252,034, which issued to DeBruyne on Feb. 24, 1981, describes a free-floating planetary transmission with a reversible output. The planetary transmission is provided with free-floating compound planetary gear elements in which two of the planet gears of each planetary element mesh with a pair of gears coaxial with the transmission axis. The transmission also includes selectively operable clutch and brake means for connecting either of said pair of coaxial gears to the transmission output while the other of said pair of gears is connected to a fixed structure thereby providing the transmission with a reversible output.
U.S. Pat. No. 4,338,525, which issued to Kilgore on July 6, 1982, discloses a marine propulsion system that includes a gas turbine, an alternating current generator, a fixed pitch propeller, a synchronous motor and a frequency converter. The frequency converted is connected electrically between the generator and motor during starting and reversal procedures when the motor would normally have to operate as an induction motor. Means are also provided to brake the system dynamically to speeds within the capacity of the frequency converter. At speeds within the frequency converter's design capacity, the motor can be operated synchronously while it is running at a speed below the minimum operating speed of the turbine and generator.
Many different types of marine transmissions, or reverse reduction gear boxes, are available to perform the functions described above. However, when certain types of prime movers, such as engines with a high brake mean effective pressure, or BMEP, certain problems are encountered when attempting to perform crash reversal procedures. Although high BMEP engines provide certain significant advantages, such as a high horsepower to weight ratio, they exhibit a torque/RPM characteristic which is disadvantageous when the need arises to rapidly engage the engine to the propeller shaft when the engine is operating at a low rotational speed and the propeller is experiencing significant windmill forces due to the forward movement of the marine vessel through the water. These are precisely the circumstances encountered by a marine reduction gear box when a crash reversal from full ahead to full astern is commanded. These problems are typically solved by incorporating a controllable pitch propeller in the marine vessel. By specifying a controllable pitch propeller, stalling of the prime mover can possibly be avoided during crash reversal operations by having the engine constantly under a partial load. However, this solution to the problem requires additional capital cost and a more expensive propulsion system than would otherwise be required. Therefore, a significant benefit could be achieved if a means were provided to avoid stalling of high BMEP engines during crash reversal operations without having to specify a controllable pitch propeller.